應用於高載子遷移率半導體的多層金屬歐姆接觸製作與分析

Abstract

在未來元件微縮下已經達到極限，三五族半導體是目前最有機會取代矽做為未來電晶體的材料，而元件中的Source/Drain接觸電阻也隨著元件縮小後變成影響電性好壞的關鍵，所以如何製作出良好的歐姆接觸顯然非常重要。本文將以三五族半導體為研究材料，因InGaAs電子遷移率比矽快十倍，而GaSb電洞遷移率也比矽及半導體材料高出許多，所以選擇了以N型半導體InGaAs、P型半導體GaSb作為此研究的基板材料。另外為了解決歐姆接觸良率差的困境，新研發成功的兩種CTLM量測模型，未來在半導體與金屬接觸上研究，可提高製作結果的良率，其中第一種研發CTLM模型以InGaAs、GaSb作為基材，以W/TiN/Ti合金做為金屬材料，研究出N型InGaAs特徵電阻 =2.9E-7Ωcm2的表現，P型GaSb方面特徵電阻為 =3.8E-5Ωcm2。而第二種CTLM模型以GaSb為基材，利用蒸鍍方式來做為沉積金屬薄膜方法來製作，金屬材料運用了Ni與Co兩種金屬材料做研究，半導體方面選擇P型 GaSb，分別摻雜Si和未摻雜做比較，分別在溫度未退火與200℃~500℃做退火幾個不同條件下做研究，結果分析發現有摻雜的GaSb並沒有較好特性，而三組樣本都在500℃退火後，表面形貌極度變差，並且在研判與NiSb、Ni2Ga2或CoGa、CoSb2的反應相有關，因此我們認為GaSb若以單層金屬Ni、Co並不適合500℃以上合金退火。

III-V material is one of the most promising alternative channel materials to replace silicon in the future nano-scaled transistors. The reduction of source/drain contact resistance is becoming essential to obtain high device performance when gate length has been continuously shrunk down. In this work, we use InGaAs and GaSb as N-type and P-type semiconductors for contact fabrication, respectively. InGaAs can provide significantly higher electron mobility compared with silicon and the hole mobility of GaSb is also higher than silicon. In order to solve the difficulties of achieving low ohmic contact resistance, we have developed two new methods for CTLM structure formation. In these new methods, we can have more metal choices in the structure while the fabrication process is simple. The first CTLM structure combines both PVD and CVD techniques to deposited TiN/Ti and W as multi-layered metal stack. The resulting specific contact resistances are ρc = 2.9E-7Ωcm2 for InGaAs and =3.8E-5Ωcm2 for GaSb, repectively. It is believed that the lower ρc can be expected when ion Implantation is further introduced with optimized conditions. The other CTLM method uses the evaporation technique to deposit metal film in the contact structure. We have studied Ni and Co for metal materials on P-GaSb substrates. Si-doped and undoped GaSb schemes were adopted for experimental comparison. The annealing temperatures are ranging from 200 ℃ ~ 500 ℃. Structures with metals on Si-doped GaSb do not show significant specific contact resistance improvement. Moreover, the roughnesses of the samples become extremely high after 500 ℃ thermal annealing. This may be caused by the phase formation of NiSb、Ni2Ga2、CoGa、CoSb2. As a result, the alloy of Ni or Co metal on GaSb should be carefully performed at temperatures lower than 500 oC during thermal annealing.